The present invention relates to a process for the dimerization of propylene and the n-butylenes by reaction in the presence of a heterogeneous palladium cyanide catalyst.
The mono-olefinic dimers of propylene and the n-butylenes have recognized utility as intermediates in the synthesis of lubricants, plasticizes and surface active agents, particularly alcohols and alkylates. In the past, commercial production of mono-olefins in the C.sub.6 to C.sub.8 range has largely been achieved through the catalytic oligomerization of ethylene. Economic incentive has developed, however, for the use of other feedstocks, particularly propylene and the butylenes.
Under common conventional practice, propylene and butylene have been converted to dimers by reaction in the presence of a strong acid, particularly sulfuric acid, phosphoric acid, or boron trifluoride. The products of such conversions have substantial branching in the dimer molecules. An object of the present invention is a process which is selective in the production of dimers having limited branching in the molecular structure.
With regard to general aspects of the present invention relating to propylene and butylene dimerization reactions catalyzed by palladium salts, it is known in the art (U.S. Pat. No. 3,758,626 to R. P. Arganbright) that dimerization of olefins can be accomplished in the presence of palladium halide, sulfate or nitrate salts supported on materials such as alumina or silica alumina. Palladium chloride and palladium nitrate are said to be particularly preferred, and no mention is made in the patent of the use of palladium cyanide. Experimental examples indicate very low levels for conversion of propylene to its dimers.
A. D. Ketley et al (Inorganic Chemistry, Vol. 6, No. 4, April 1967, pp. 657-663) also disclose the dimerization of propylene by palladium chloride. The catalysis is homogeneous with the palladium chloride present as a complex with propylene in solution together with a solvent such as CCl.sub.4, C.sub.2 H.sub.5 Cl, t-C.sub.4 H.sub.9 Cl, CHCl.sub.3, CH.sub.2 Cl.sub.2, or anisole. The products of this dimerization are strongly dependent upon the nature of the solvent.
With regard to more particular aspects of the invention relating to a palladium cyanide catalyst, it is further known from the above-referenced publication of Ketley et al and from U.S. Pat. No. 3,535,302 to Ketley that ethylene can be dimerized in the presence of palladium cyanide. However, when propylene was utilized as a reactant instead of ethylene, the publication and the patent indicate that a reaction either with or without a solvent yields only a polymeric product. No reaction was observed for butylenes.
Y. Odaira et al (J.A.C.S., Vol. 88, No. 17, Sept. 5, 1966, p. 4106) disclose that the reaction of propylene in the presence of palladium cyanide and a polar solvent yields the cyanation products HCN, methacrylonitrile, 3-butenenitrile, crotononitrile, isobutyronitrile, and butyronitrile. In nonpolar solvents, Pd(CN).sub.2 was said to lead almost exclusively to the conversion of propylene to high polymers.
A. Sen et al (J.A.C.S., 1981, Vol. 103, p. 4627; Organometallics, 1982, Vol. 1, p. 415; and a paper presented to the August 1981 International Symposium on Transition Metal Catalyzed Polymerization: Unsolved Problems) have recently reported that certain metal complexes, including Pd(CH.sub.3 CN).sub.4 (BF.sub.4).sub.2, are active as homogeneous catalysts for the dimerization, oligomerization, and polymerization of olefins, apparently to relatively highly branched product molecules.